1. Field of the Invention
The present invention relates to a disc brake for use in a vehicle such as an automobile.
2. Prior Art
There has recently arisen a pronounced desire for an improvement in a rate of fuel consumption of automobiles. Various measures have been attempted to improve the rate of fuel consumption. One of them is to improve power-supply system performance by improving engine performance. Another is to reduce running-resistance through improvements in the design of vehicle bodies. It is also known that reducing resistance to acceleration when accelerating a car greatly contributes to an improvement in the rate of fuel consumption. There have also been various attempts to reduce the weight of vehicles which has a direct influence on the rate of fuel consumption.
Reducing the weight of a disc brake which is provided on a car has been attempted as one measure for reducing the weight of a vehicle. This attempt relates to a caliper which comprises one part of a floating type of disc brake. The caliper comprises a cylinder member having a cylinder bore formed therein for receiving a piston for forcing an inner pad onto a disc, and a claw member having a disc-passing portion straddling the disc and a claw portion for abutting an outer pad to force it onto the disc. The cylinder member is provided with through-holes extending in the axial direction of the disc while corresponding tapped holes are formed in the disc-passing portion of the claw member. Respective bolts are inserted through the through-holes and are threaded into the tapped holes to fixedly secure the cylinder member and claw member to each other. Although the claw member is made of iron, the cylinder member is made of a light alloy such as an aluminum alloy, thereby reducing the weight of the caliper. It is necessary for the claw member to be made of iron in order for it to be highly rigid in order to withstand substantial forces. Namely, a very great force acts on the claw member when the brake is actuated and the claw portion is forcing the outer pad onto the disc. There is also a requirement for the disc-passing portion to be formed with a thickness not exceeding a certain value which is determined from the design requirements, since the disc-passing portion is located within a narrow area of clearance between the disc and the wheel associated therewith. Consequently, the claw member is made of iron which, although relatively thin, is highly rigid.
However, the conventional caliper mentioned above suffers from the following problems.
When the caliper is actuated to force the pads onto the disc, a great lateral force acts on the bolts securing the cylinder member and claw member to each other, and distorts respective portions of the two members engaged with each other as well as the bolts. If bolts with a larger diameter are employed to connect the cylinder member and claw member in order to provide for stronger securement of the two members so as to prevent distortion of the associated members, the disc-passing portion of the claw member must be made thicker, thus causing the disc to be smaller in diameter. This disc with a reduced diameter leads to a deterioration in braking performance. The disc with a reduced diameter does not have a sufficient heat capacity, either. When smaller diameter bolts are employed in order to avoid causing the diameter of the disc to be made smaller while attaining sufficient strength of the securing means, the number of bolts must be increased. This leads to an increase in both the number of parts of the disc brake and the number of steps required for its assembly, resulting in high production costs.